The present invention relates generally to magnetic levitation devices and more particularly to magnetic levitation self-regulating systems comprising permanent magnets and ferromagnetic cores capable of providing the stable hovering of a working body in a magnetic field without any active control system.
In the year of 1839 S. Earnshaw published a theorem [S. Earnshaw: Trans. Cambridge Philosophical Society 7. 97-112 (1839)]. It states that charged bodies in any electrostatic field do not have a stable equilibrium position when they are solely under the influence of electrostatic forces. One hundred years later W. Braunbek [W. Braunbek: Z. Physik. 112 753-763 (1939)] extended Earnshaw's theorem to magnetostatic fields. Proofs of these theorems are based on the properties of the scalar potential of a static field. Such a potential, being a solution of Laplace's equation, cannot have an extrema in any inward point of a field. It is important to note that both of these theorems hold true for a system of free bodies placed in a field. In this case, any body in the field will drift along the lines of force toward the field borders (i.e. conducting or ferromagnetic surfaces) until contacting the border.
However, if bodies are connected with each other by non-conducting or non-magnetic couplers and placed in independent fields, it is obvious that they cannot move freely along the lines of force. To describe their movement it is necessary to complete Laplace's equation (with appropriate boundary conditions) with the equations for the couplers. Thus, the theorems mentioned above are not correct under these circumstances.
Unfortunately, this important realization concerning Laplace's equation was unrecognized, and these theorems are still used today to assert the impossibility of creating a stable levitation system consisting of charged or magnetic bodies in an electrostatic or magnetostatic field regardless of whether there are couplers between them or not. Consequently, designers have concentrated on the improvement of automatic control systems to provide stability of levitation rather than conducting research concerning as yet unknown principles of self-regulation that would allow self-regulating magnetic levitation systems to be created.
Langrange's theorem is used to determine the stability of the equilibrium position of any conservative system. [Pol Appell: Traite de Mecanique Rationnelle. Paris, Gauthier-Villars, Etc. Editeurs ]. The theorem states that if at a certain position of a conservative system, the potential energy has a strict local minimum, then that position is a stable equilibrium point of the system. It is worth noting that this theorem and the two cited above do not contradict one other. Lagrange's theorem covers a broader range of cases then the earlier cited theorems. Specifically, it can be applied to a conservative system with couplers.
It is known that the existing magnetic levitation systems of the electromagnetic type use iron cores and electromagnets with an air gap here between. The magnets do not have an equilibrium position therein, and the magnetic field is distributed in such a way as to create destabilizing forces only, tending to attract the magnets to the iron cores.
In order to provide stability to the known systems, a fast-response, automatic control system is necessary. Such control is expensive to provide and has up until now not been very reliable.
The magnetic levitation self-regulating systems of the present invention use quite different elements from the known systems and include split iron cores with an air gap between their shoes rather than solid cores. Furthermore the present invention uses permanent magnets rather than electromagnets. This structure provides an equilibrium position for permanent magnets in the air gap and the distribution of the magnetic field therein is capable of creating both stabilizing and destabilizing forces.
A linear synchronous motor having variable pole pitches is disclosed in U.S. patent application Ser. No. 691,430, a linear synchronous motor having enhanced levitational forces U.S. patent application Ser. No. 764,734, a selfadjusting magnetic suspension for a levitated vehicle guideway U.S. patent application Ser. No. 691,431, serve as examples of these elements.